The present invention relates to a hydraulic striking device, and more particularly to a hydraulic striking device of the type that includes a pressure conduit for receiving hydraulic fluid under pressure, a return conduit for releasing the hydraulic fluid at a lower pressure, a percussion piston which is movable in an operating cylinder and which has two annular faces of different sizes and a circumferential groove between the faces, the faces being charged to move in opposite directions, a bit which is struck by the percussion piston, a valve body which is movable in a control valve and which has different sized partial faces which can be charged perpendicularly to the direction of movement, wherein the smaller face of the percussion piston is constantly connected to the pressure conduit and the larger face of the piston is alternately connected via the control valve with the pressure conduit and the return conduit, and wherein the smaller partial face of the valve body is constantly connected to the pressure conduit and the larger partial face of the valve body is alternately connected via the circumferential groove of the percussion piston with the pressure conduit and the return conduit.
Such devices are known, for example, from German Ausleggeschrift (published patent application) No. 2,428,236. In these devices, the percussion piston, before reaching either one of its two end positions, emits a control pulse of fluid which initiates the switching of a control valve which, in turn, causes the forces acting on the percussion piston to be reversed. The control pulses, which are a function of the path traversed by the percussion piston, are selected in such a manner that the percussion piston, in view of the switching delay of the control valve, on the one hand comes to rest at the intended upper reversal point and then begins its operating stroke and, on the other hand, is subjected to the forces causing the return stroke after the piston has struck the bit.
If, in the prior art striking device, striking energy is reflected from the tip of the bit, the percussion piston is accelerated in the direction of the return stroke and the control conduit, having been opened by the percussion piston, is closed again so that the switching pulse for the control valve is interrupted. The control valve then continues to remain in the position at which the percussion piston is charged toward the bit. The back-reflected percussion piston is thus decelerated and then accelerated again toward the bit. A so-called "double strike" occurs. Such double strikes are extremely undesirable and disadvantageous since, on the one hand, they effectively interfere with the quiet operation of the striking device and, on the other hand, reduce the number of strokes during which the percussion piston is accelerated from its upper or rearward reversal point.